Bitterness is one of the important characteristics that distinguishes beer from other alcoholic beverages. The bitterness in beer comes from hops. Generally, the normal bitterness of beer will disappear quickly, giving people a refreshing feeling after drinking, without leaving any bitter aftertaste. However, in the production process of beer, if the process conditions are not perfect, the quality of the raw materials is defective, and the process hygiene is poor, the bitterness of the beer will become rough, bitter, and have a long aftertaste.
The solubility of alpha acids in hops in water is very low. After boiling, alpha acids undergo isomerization reaction to obtain isomerized alpha acids, which can be dissolved in water. Isomerized alpha acids contribute 80% of the bitterness in beer. Therefore, the amount of isomerized alpha acids generally determines the bitterness of beer. The unit for measuring the concentration of isomerized alpha acids is called International Bittering Units (IBU for short). The longer the hops are boiled, the higher the concentration of isomerized alpha acids, and the higher the IBU; when other conditions remain unchanged, it will taste more bitter. The IBU of beer is usually between 5 and 110, and anything above 80 is considered very bitter.
IBU is obtained by measuring the absorbance of the sample under ultraviolet light at a wavelength of 275nm. The commonly used method is high-performance liquid chromatography (HPLC). Since HPLC has high requirements for measuring equipment, most craft breweries measure it through UV spectrophotometry with lower accuracy, or estimate IBU through formulas.
Even if the IBU is accurately measured, it cannot reflect the actual perceived bitterness. In addition to isomerized alpha acids, other substances in beer can also bring bitterness. For example, when dry hopping, no isomerized alpha acids are added, but alpha acids, oxidized alpha acids, oxidized beta acids and phenolic substances are increased, all of which bring bitterness, but the narrow IBU does not reflect the content of these substances. The residual sugar content in beer is also an important factor affecting the perceived bitterness. Although some beers have a high IBU, they do not taste too bitter because of the high residual sugar. Therefore, more and more craft breweries, bars, and this book choose not to mark IBU.
